Rotating machines are already known wherein the rotors include tangential magnets which are placed around the periphery of the rotor and are radially magnetized. These machines provide an inductive excitation which is relatively weak because of the nature of the magnets and because of their relatively low level of operation. On the other hand, a high linear density current can be provided in the stator, and the magnetic armature reaction in the rotor remains low because the magnets, which are the major component of the periphery of the rotor, are equivalent to an appreciable air gap.
Because of the weak excitation induction provided, the generated torque is limited to low values, despite the high linear current density.
To raise the excitation induction level, i.e., in order to increase the inductive forces generated, machines have been proposed wherein the rotor has radial portions joined by polar masses which concentrate the magnetic flux in the direction of the air gap. Such machines feature a high inductive excitation as a result of the concentration of the flux, which is additionally increased because the total surface of the magnets can be greater than the surface area of the air gap beyond a certain number of poles.
On the other hand, only a relatively low linear current density can be provided in the stator due to the fact that the magnetic armature reaction increases rapidly, because these machines have a small air gap and the pole masses reduce the distance covered by the lines of magnetic field produced by the stator currents. The result is that the torque which can be generated with such machines is also limited to low values and cannot be greatly increased.
A number of rotating machines with magnets have been proposed wherein the pole pieces include different kinds of recesses or the like. However, the purposes of these recesses are completely different from that of limiting of the armature reaction flux, and thus the use of these recesses is completely different from that of the invention. For example, French Pat. No. 2 162 595 describes a machine with magnets on the rotor in which slots are provided in the pole pieces to limit the magnetic excitation flux and to direct this flux radially. This arrangement inhibits the propagation of the excitation flux in the central and largest part of the pole pieces, while, as explained below, in accordance with the present invention, a high excitation is sought, together with a limitation on the armature reaction flux.
German Patent Application No. 2 062 486 describes a machine with magnets on the rotor in which the recesses are arranged in the pole pieces in the vicinity of the centripetal base of the pole pieces. The object there is to obtain a regulation capability for the state of saturation and thus to influence the magnetic resistance in the main circuit. Such an arrangement will not satisfactorily oppose the propagation of armature fluxes in most of the pole piece.
Japanese Pat. No. 51-127 404 describes a synchronous motor of a construction intended to resist demagnetization of the continuous stator magnetic flux. The flux is shunted through a passage in the central part of the pole pieces but without interruption. The pole pieces hve small circular obstacles provided on their peripheries but these cannot oppose the greater part of the armature reaction flux in the pole piece.
French Pat. No. 1 313 993 describes a rotary machine with magents and including a relatively large recess in the pole pieces filled with a nonmagnetic material and intended to facilitate manufacture of the rotor and to decrease the weight thereof. However, such a large recess in the surface area is an obstacle to the satisfactory propagation of the excitation flux. Moreover, in such a device, which includes a great number of magnets so that the pole pieces are of relatively small angular amplitude, the reaction flux tends to be concentrated in the peripheral part of the pole pieces, where the aforementioned recess does not extend.
French Pat. No. 1 303 243 describes a rotor provided with a great number of permanent magnets placed in such a manner as to inhibit the passage of the armature reaction flux. This is an extremely complex and costly construction and because of this, suffers substantial drawbacks.
German Application No. 1 563 040 also describes a rotor having a great number of magnets which inhibit the propagation of armature reaction flux and which, between them, define pole pieces of small angular amplitude. Such an arrangement exhibits substantially the same characteristics as that of French Pat. No. 1 313 993.